Active grounded thermocouple and method of operation

ABSTRACT

An active temperature measurement system includes at least one grounded thermocouple and a processor in communication with the at least one grounded thermocouple. The processor is configured to receive measurements from the at least one grounded thermocouple. The at least one grounded thermocouple is biased by an isolated voltage when the processor is receiving a measurement from the at least one grounded thermocouple.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patentapplication Ser. No. 62/155,559 filed on May 1, 2015, the entirecontents of which are incorporated herein by reference in theirentirety.

FIELD

This disclosure relates generally to temperature measurement systems.More specifically, this disclosure relates to temperature measurementsystems utilizing one or more grounded thermocouples

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

A thermocouple is a sensor used to measure temperature. Thermocouplesgenerally include two wires made from dissimilar materials. The wiresare welded together at one end, creating a junction. When a junctionexperiences a change in temperature, a voltage is created. This voltage,in turn, can then be interpreted to calculate the temperature at thejunction point.

There are generally three types of thermocouples used when measuringtemperature—exposed thermocouples, grounded thermocouples, andungrounded thermocouples. An exposed thermocouple has junction outsidethe probe wall or sheath and is therefore directly exposed to the targetmedium. These types of thermocouples have excellent heat transfer andquick response times but are limited by the type of target media whenthey can be used. Generally, these thermocouples are not suitable forcaustic or corrosive environments.

For ungrounded thermocouples, the sensing junction of this type ofthermocouple is physically located within a sheath, but is electricallyisolated from the sheath. This results in a slow response time, but hasthe advantage in that the electrical isolation provided by not beingconnected to the sheath gives these thermocouples more accuratemeasurements due to reduced noise. These thermocouples can also be usedin caustic or corrosive environments and are more robust, as the sheathprovides protection from the environment.

Grounded thermocouples also utilize a sheath but have the junction indirect electrical contact with the sheath. These thermocouples have afaster response time than ungrounded thermocouples and can be used incaustic or corrosive environments. However, these thermocouples aregenerally susceptible to electrical noise, such as ground loops, whichimpacts accuracy, especially when measuring small variations intemperature.

SUMMARY

The present disclosure provides a temperature measurement system thatincludes at least one grounded thermocouple and a processor incommunication with the at least one grounded thermocouple. The processoris configured to receive measurements from the at least one groundedthermocouple. The at least one grounded thermocouple is biased by anisolated voltage when the processor is receiving a measurement from theat least one grounded thermocouple.

In another form, a plurality of thermocouples is provided. In this form,only one of the plurality of grounded thermocouples is biased with theisolated voltage when the processor is receiving a measurement from theone grounded thermocouple. The other thermocouples are unbiased anddisconnected from the isolated voltage.

In still another form, the temperature measurement system may include amultiplexer. The multiplexer is configured to provide measurements takenfrom one of the plurality of thermocouples to the processor. Inaddition, the multiplexer may be further configured to bias at least onegrounded thermocouple with the isolated voltage when the processor isreceiving a measurement from the at least one grounded thermocouple.

In another form, the temperature measurement system may include ananalog-to-digital converter in communication with the processor and theat least one grounded thermocouple. The analog-to-digital converter isconfigured to convert measurements from the at least one groundedthermocouple to digital numbers and provide the digital numbers to theprocessor.

In still another form, the at least one grounded thermocouple mayutilized a single signal wire. In this form, the at least one groundedthermocouple includes a sheath having an open end and a closed distalend having a tip. The tip of the closed distal end defines a junction.The signal wire extends from the open end to the junction point. Thesignal wire and the sheath are made from dissimilar metals configured toproduce an electric potential related to the temperature at the junctionpoint across the signal wire and the sheath.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1A is a schematic representation of a grounded thermocoupleutilizing two wires;

FIG. 1B is a schematic representation of a grounded thermocoupleutilizing a single wire;

FIG. 2A is a block diagram representation of a temperature measurementsystem utilizing grounded thermocouples in accordance with the teachingsof the present disclosure;

FIG. 2B is a block diagram representation of a temperature measurementsystem utilizing grounded thermocouples having integrated electronics inaccordance with the teachings of the present disclosure;

FIG. 3. is an electrical schematic representation of a power supply forthe temperature measurement system utilizing grounded thermocouples inaccordance with the teachings of the present disclosure;

FIGS. 4A and 4B is an electrical schematic representation of thetemperature measurement system utilizing grounded thermocouples inaccordance with the teachings of the present disclosure;

FIG. 5 is a perspective view of a heating apparatus incorporating thetemperature measurement system utilizing grounded thermocouples inaccordance with the teachings of the present disclosure;

FIG. 6 is another perspective view of the heating apparatusincorporating the temperature measurement system utilizing groundedthermocouples in which the outer exhaust system coupling components havebeen removed in accordance with the teachings of the present disclosure;

FIG. 7 is another perspective view of the heating apparatusincorporating the temperature measurement system utilizing groundedthermocouples in which the outer exhaust system coupling components havebeen removed in accordance with the teachings of the present disclosure;

FIG. 8 is a perspective cross-sectional view of the heating apparatus ofFIG. 6 in accordance with the teachings of the present disclosure;

FIG. 9A is an enlarged perspective cross-sectional view of portion A ofFIG. 8 in accordance with the teachings of the present disclosure; and

FIG. 9B is a perspective view of a thermowell and an groundedthermocouple with the heating apparatus in accordance with the teachingsof the present disclosure.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is in no wayintended to limit the present disclosure or its application or uses. Itshould be understood that throughout the description, correspondingreference numerals indicate like or corresponding parts and features.

The present disclosure generally relates to a temperature measurementsystem and a method of use associated therewith. The temperaturemeasurement system made and used according to the teachings containedherein is described throughout the present disclosure in in numerousapplications. One of these applications includes diesel exhaust systems.This is just but one application of the temperature measurement systemand the incorporation and use of temperature measurement system inconjunction with other types of thermal management applications iscontemplated to be within the scope of the disclosure.

The following specific forms are given to illustrate the design and useof temperature measurement systems according to the teachings of thepresent disclosure and should not be construed to limit the scope of thedisclosure. Those skilled-in-the-art, in light of the presentdisclosure, will appreciate that many changes can be made in thespecific forms which are disclosed herein and still obtain alike orsimilar result without departing from or exceeding the spirit or scopeof the disclosure. One skilled in the art will further understand thatany properties reported herein represent properties that are routinelymeasured and can be obtained by multiple different methods. The methodsdescribed herein represent one such method and other methods may beutilized without exceeding the scope of the present disclosure.

Referring to FIG. 1A, a grounded thermocouple 10A is shown. Here, thegrounded thermocouple 10A includes a first wire 12A and a second wire14A. The first wire 12A and second wire 14A are connected to one anotherat a junction 16A. Generally, the first wire 12A and the second wire 14Aare made of dissimilar metals. These dissimilar metals may include awide range of materials, such as iron, nickel, copper, chromium,aluminum, platinum, rhodium and their alloys. Of course, it should beunderstood that any type of material suitable for the construction ofthermocouple may be utilized when selecting the dissimilar metalsutilized in constructing the first wire 12A and the second wire 14A.

The grounded thermocouple 10A may also include an insulator 17A. Theinsulator 17A surrounds and protects portions of the first wire 12A andthe second wire 14A. The insulator 17A may be useful if the thermocouple10A is utilized in high moisture and pressure in corrosive environments.The insulator 17A may be made of magnesium oxide; however, any othersuitable material may also be utilized. Encapsulating the insulator 17A,the first wire 12A and the second wire 14A is a sheath 18A. The sheath18A provides protection to the insulator 17A as well as the first wire12A and the second wire 14A.

When a temperature measurement is taken at the junction 16A, thedissimilar metals of the first wire 12A and the second wire 14A willproduce a voltage difference that is related to temperature. Using areference table that contains a representative voltage that relates tospecific temperature, one can determine the temperature at the junction16A.

Referring to FIG. 1B, another version of the thermocouple 10B is shown.It should be understood that like reference numerals have been utilizedto refer to like elements. As such, any description previously given isequally applicable. Here, the thermocouple 10B utilizes a single wireconfiguration. More specifically, there is a single wire 12B inconnection with the junction 16B. As stated previously, in order for athermocouple to work properly, there must be two dissimilar materialsutilized so as to create a voltage difference representative of thetemperature. In this form, the dissimilar material utilized is found inthe sheath 18B. Essentially, as the wire 12B is connected to the sheath18B at the junction 16B, a voltage difference can be measured betweenthe wire 12B and the sheath 18B. As such, unlike the configuration shownin FIG. 1A, this configuration allows for a single wire to be utilizedin reading a voltage representative of temperature.

It should be understood that the foregoing description may utilizeeither thermocouple or combination thereof. As such, going forward withthis description, it should be understood that any mention of the wordthermocouple in this description can relate to either the thermocouplesdescribed in FIG. 1A or 1B.

Referring to FIG. 2A, a block diagram of the system 20 for measuringtemperature is shown. As its primary components, the system 20 includesa processor 22, an analog-to-digital converter 24, a multiplexer 26, andbus controller 28. The system 20 also includes thermocouples 10X, 10Y,and 10Z. As stated before, the thermocouples 10X, 10Y, and 10Z may beany of the thermocouples previously described in this description. Also,it should be understood that the thermocouples 10X, 10Y, and 10Z mayjust be one thermocouple or may be numerous thermocouples and should notbe limited to three thermocouples as shown. The thermocouples 10X, 10Y,and 10Z may be active thermocouples having integrated electronics.

Here, the thermocouples 10X, 10Y, and 10Z are in communication with themultiplexer 26. The multiplexer 26 functions to multiplex data receivedfrom the thermocouples 10X, 10Y, and 10Z. Essentially, the multiplexer26 will transmit to the analog-to-digital converter 24 informationrelating to the thermocouples 10X, 10Y, and 10Z, so as to eliminatemultiple connections to the analog-to-digital converter 24.

The analog-to-digital converter 24 will then convert data received fromthe multiplexer 26, which originated with the thermocouples 10X, 10Y,and 10Z to a digital number. This digital number is then provided to theprocessor 22 for further processing. The processor 22 may communicatewith other systems via a bus controller 28. If, for example, the system20 is utilized in an automobile, the bus controller 28 may be aController Area Network (CAN) type bus.

Grounded thermocouples, such as thermocouples 10X, 10Y, and 10Z, havethe advantage of rapid response times to temperature changes, but havethe disadvantage in that they are susceptible to electrical noise, suchas a ground loop. To inhibit such a ground loop with the power supply ofthe thermocouples 10X, 10Y, and 10Z, isolation is generally provided tothe thermocouples 10X, 10Y, and 10Z and then the measurement generatedby the thermocouples 10X, 10Y, and 10Z is made.

The system 20 utilizes an isolated voltage 30 for biasing as well as anisolated ground 31. The isolated voltage 30 and the isolated ground 31are separate from the supply voltage and ground voltage from any otherunderlying system. For example, if the system 20 is utilized anautomobile, the isolated voltage 30 and isolated ground 31 are separateand apart the positive terminal supply voltage of the automobile and theground provided by the chassis of the automobile.

This isolated voltage 30 biases the thermocouples 10X, 10Y, and 10Z, theprocessor 22, the analog-to-digital converter 24, and the multiplexer26. As for grounding, the thermocouples 10X, 10Y, and 10Z, the processor22, the analog-to-digital converter 24, and the multiplexer 26 aregrounded to the isolated ground 31.

However, additional isolation is also provided to the thermocouples 10X,10Y, and 10Z. In this example, the thermocouples 10X, 10Y, and 10Z willonly be biased with the isolated voltage 30 when a desired measurementis taken by one of the thermocouples 10X, 10Y, or 10Z. Morespecifically, when a measurement is taken from thermocouple 10X, theisolated voltage will bias the thermocouple 10X and not thermocouples10Y, and 10Z. In like manner, if a measurement is taken of thermocouple10Y, the isolated voltage will be applied to thermocouple 10Y andremoved from thermocouples 10X and 10Z. Similarly, if a measurement istaken of thermocouple 10Z, the isolated voltage will bias thermocouple10Y and removed from thermocouples 10X and 10Y.

This methodology is taking advantage of the fact that each of thethermocouples 10X, 10Y, and 10Z will likely be attached to the sameground, such as the chassis of an automobile, and will have roughly thesame relative voltages. If all of the thermocouples 10X, 10Y, and 10Zwere biased at the same time by the isolated voltage 30, the relativevoltages could result in noise currents between the thermocouples 10X,10Y, and 10Z. Because of the very small signal levels being measuredfrom the thermocouples 10X, 10Y, and 10Z, these small variations willcause measurement errors. The advantage to the system 20 is the nothaving to fully isolating each thermocouple, as only one of thethermocouples 10X, 10Y, or 10Z will be biased.

Referring to FIG. 2B, as stated previously, the thermocouples 10X, 10Y,and/or 10Z may be active thermocouples having integrated electronics.For example, one or more of the thermocouples 10X, 10Y, and/or 10Z mayincorporate electronic components. More specifically, one or more of thethermocouples 10X, 10Y, and/or 10Z may include a housing 47 thatcontains the processor 26, the analog-to-digital converter 24, and/orthe multiplexer 22. In addition to these and components, the housing 47of one or more of the thermocouples 10X, 10Y, and/or 10Z may include thepower supply 44 described in the following paragraphs.

Referring to FIG. 3, a power supply 40 for the measuring system 20 isshown. The power supply 40 includes a voltage input 42. This voltageinput 42 may be connected to the positive voltage terminal of a batteryof an automobile. Voltage provided to the voltage input 42 is thenprovided to overvoltage protection portion 44 of the power supply 40.Overvoltage occurs when the voltage in a circuit is raised above itsupper design limit. Depending on its duration, the overvoltage event canbe transient—a voltage spike—or permanent, leading to a power surge.

The overvoltage protection portion 44 in one form includes a diode 46for protecting a source connected to the voltage input 42. In addition,a transistor 48 is connected in series with the diode 46. In addition tothese two elements, the overvoltage protection portion 44 includes otherelectrical elements as shown in FIG. 3 for both signaling andconditioning. When connected as shown, the diode 46, transistor 48, andother components provide overvoltage protection to the power supplyportion 46 of the power supply 44.

The power supply portion 46 of the power supply 44 is responsible forgenerating the isolated voltage and ground provided to the system formeasuring temperature 20. The power supply portion 50 includes aregulator 52. The regulator 52 acts as a regulator for regulating anoutput voltage, such as the isolated voltage provided to the system formeasuring temperature. The regulator 52 may be, for example, an LM5019regulator produced by Texas Instruments, Inc. of Austin, Tex. Theregulator 52 has the advantage in that it is capable of producing anisolated voltage without having to provide feedback to a feedbackcircuit to monitor the isolated voltage to provide the isolated voltagewithin an expected range. The device 52 is based on a constant on timecontrol scheme using an on time inversely proportional to the inputvoltage. This control scheme may not require a loop condensation. Thecurrent limit is implemented with a forced off time inverselyproportional to the output voltage, in this case, the isolated voltage.This scheme provides short circuit protection while providing minimumfeedback. The power supply portion 50 outputs an isolated voltage 30, aswell as an isolated ground 31. Both the isolated voltage 30 and isolatedground 31 are provided to the system for measuring temperature 20.

Referring to FIG. 4A, this figure illustrates a circuit schematicshowing thermocouples 10X, 10Y, and 10Z, as well as multiplexer 26.Here, the thermocouples 10X, 10Y, and 10Z are biased by the isolatedvoltage 30. In addition, the multiplexer 26 is also biased by theisolated voltage 30. As stated before, only one of the multiplexers 10X,10Y, or 10Z, may be biased by the isolated voltage 30. This bias onlyoccurs to one of the thermocouples 10X, 10Y, and 10Z, when the selectedthermocouple is taking a measurement. Application of the isolatedvoltage 30 to the thermocouples 10X, 10Y, or 10Z can occur through avariety of different methodologies. In this example, the multiplexer 26has the ability to provide the isolated voltage 30 to only one of thethermocouples 10X, 10Y, and 10Z when a reading is being performed. Asstated before, the multiplexer 26, depending on which thermocouple isbeing utilized, will output to an output line 54 an analog signalrepresentative of the temperature measured by one of the thermocouples10X, 10Y, or 10Z.

Referring to FIG. 4B, this figure shows schematic circuit representationof the analog-to-digital converter 24, processor 22, and the networkcontroller 28. Here, this example includes two separateanalog-to-digital converters 24A and 24B, as well as two separatenetwork controllers 28A and 28B. It should be understood that it ispossible that only a single analog-to-digital converter 24A or 24B couldbe utilized. In like manner, it should be understood that a singlenetwork controller 28A or 28B could also be utilized. Similarly, anynumber of converts and controllers may be used while being within thescope of the present disclosure.

Regardless of the number of analog-to-digital converters utilized, bothanalog to digital converters 24A and 24B each have the isolated biasvoltage 30 applied to them as well as an isolated ground 31. Theanalog-to-digital converters 24A and 24B receive the analog signal fromline 54 from the multiplexer 26 and convert the analog signal to adigital number. This digital number is in turn provided to the processor22. The processor 22 may store the digital number internally or may alsoutilize a separate storage device 56, such as an EEPROM.

From there, the processor 22 may provide temperature information to abus 58. In this example, the bus 58 is a CAN bus. The CAN bus canutilize a single chip network controller, such as controller 28, or mayutilize a multichip isolated network controller, such as networkcontroller 28B. Data provided to the bus 58 can be provided to othersystems connected to the bus. If the other systems are automobilerelated, these systems may use temperature information provided by thethermocouples 10X, 10Y, and 10Z other systems, such as a heater for adiesel exhaust system.

As stated previously, the thermocouples 10X, 10Y, and/or 10Z mayincorporate electronic components. Like before, one or more of thethermocouples 10X, 10Y, and/or 10Z may incorporate electronic componentsshown and described in FIGS. 2A and 2B. More specifically, one or moreof the thermocouples 10X, 10Y, and/or 10Z may include a housing thatcontains the processor 26, the analog-to-digital converter(s) 24A and24B, and/or the multiplexer 22. In addition to these and components, ahousing of one or more of the thermocouples 10X, 10Y, and/or 10Z mayinclude the power supply 44 of FIG. 3 and/or the network controllers 28Aand/or 28B. Essentially, thermocouples 10X, 10Y, and/or 10Z have ahousing that is connected to the sheath of the thermocouples 10X, 10Y,and/or 10Z and contains any combination of the before mentionedelectronics. In addition, the housing may have a port or a set of wiresthat allow the entire thermocouple assembly to be connected to a bus,such as a CAN bus.

As stated previously, the system 20 can be utilized in any one of anumber of different applications. One such application are heatersystems are used in exhaust systems that are coupled to an internalcombustion engine in order to assist in the reduction of the undesirablerelease of various gases and other pollutant emissions into theatmosphere. These exhaust systems typically include variousafter-treatment devices, such as diesel particulate filters (DPF); acatalytic converter; selective catalytic reducers (SCR) that capturecarbon monoxide (CO), nitrogen oxides (NO_(x)), particulate matters(PMs), and unburned hydrocarbons (HCs) contained in the exhaust gas; adiesel oxidation catalyst (DOC); a lean NO_(x) trap (LNT); an ammoniaslip catalyst; or reformers, among others. The heaters may be activatedperiodically or at a predetermined time to increase the exhausttemperature and activate the catalysts and/or to burn the particulatematters or unburned hydrocarbons that have been captured in the exhaustsystem. The activation of these heaters may be determined by a processorthat receives temperature information from sensors, such asthermocouples 10X, 10Y, and 10Z and the temperature measurement system20 described above.

Referring to FIG. 5, one such system in which the teachings of thepresent disclosure may be applied is a heating apparatus 101, which inone form generally includes a junction box 105, a perforated boxassembly 110, a container body 114 including one or more separablecontainer section components 115, and a heater flange component 120.This heating apparatus 101 may be similar to a heating apparatusdescribed in published U.S. Patent Application 2014/0190151, which iscommonly owned with the present application hereby incorporated byreference in its entirety. Exhaust system coupling components 125 may beprovided at opposing ends of the container body 114 to couple theheating apparatus 101 into an exhaust system (not shown). The exhaustgases flow from the exhaust system into the heating apparatus 101through a pathway 130 formed in the heating apparatus 101. The pathway130 is defined jointly by the container body 114 and the heater flangecomponent 120. The heater flange component 120 generally has a plateconfiguration in one form. The modular design of the heating apparatus101 allows the dimensions of the various components in the heatingapparatus 101 to stay the same with only the length of each componentbeing varied to accommodate the requirement(s) of the application. Ajunction box lid 107 may be incorporated into the heating apparatus 101.In some applications, such as in a diesel exhaust system, among others,the vibrations arising from the application may be to such a degree thatat least one support bracket (not shown) may be necessary to effectivelymount the heating apparatus 101.

Referring to FIGS. 6 and 7, the heating apparatus 101 further includesone or more heater elements 135 and a bracket assembly 140. In one form,the bracket assembly 140 includes an optional upper spine component 141,one or more element support component 143, and an optional lower spinecomponent 145. In one form, the element support component 143 includes aplurality of posts 143 that are coupled to corresponding ones of theheater elements 135 and are arranged perpendicular to a longitudinalaxis X of the container body 114. The posts 143 are coupled to eitherthe container section components 115 of the container body 114 or to theoptional upper spine component 141 and lower spine component 145. Theposts 143 may be directly coupled to the heater flange component 120when desirable for applications that do not require the bracket assembly140 to have an upper spine component. The posts 143 include an optionalflow diverter 170 that blocks the flow of exhaust gas down the center ofthe pathway 130 formed in the heating apparatus 101.

The heater element 135 may exhibit predetermined (e.g., measured) orpredictable performance characteristics. One example of such performancecharacteristics includes the rate of heating for the heater element 35when it is exposed to a preselected voltage or under a specified processflow condition. The heater element 135 is selected as a cable heater, atubular heater, a cartridge heater, a flexible heater, a layered heater,a metal foil, or a metal fleece heater. Alternatively, the heaterelement 135 is a cable heater or tubular heater, or a bare wire heater,among others.

The heater flange component 120 is coupled with the one or morecontainer section components 115 of the container body 114, such thatthey form an external shroud that surrounds the one or more heaterelements 135 and establishes the pathway 130 for the flow of exhaust gasthrough the heating apparatus 101. The heater flange component 120 andthe one or more container section components 115 may contact one anotherthrough the use of tabs 121. The tabs 121 may be located on either theheater flange component 120 or the one or more container sectioncomponents 115. Each tab 121 in one component 115, 120 is mated to ahole 122 located in the other component 120, 115. The use of the tabs121 facilitates the assembling of the heater flange component 120, thebracket assembly 140, and the heater elements 135 prior to coupling theheater flange component 120 to the container body 114.

Referring now to FIG. 8A, the junction box 105 establishes an electricalconnection 109 between the heater elements 135 and a power source (notshown), while the perforated box assembly 110 provides a means to coolthe electrical connections 109 and heater elements 135 by creating alonger path for conduction and radiation heat transfer, as well as allowfor convective air cooling. The perforated box assembly 110 has at leastone wall or skirt that is perforated, thereby, exposing the interior ofthe perforated box assembly 110 to the atmosphere. The perforated boxassembly 110 is used in applications in which the magnitude of heat issuch that cooling of the junction box 105 is required. One skilled inthe art will understand that the perforations present in the wall orskirt may represent one or more perforations with each perforation beingof any size or shape.

The heating apparatus 101 may further include one or more standoff tubes60 that project from the perforated box assembly 110 through the heaterflange component 120 into the external shroud formed by the containersection components 115. Each standoff tube 160 encompasses a heaterelement 135 to provide mechanical support for the heater element 135.One or more of the top and bottom of the optional perforated box, thewalls of the perforated box and the standoff tubes may be brazedtogether using nickel or copper. When desirable, one skilled in the artwill understand that it is possible to braze the heater elements 135directly to the junction box 105 and the optional perforated box 110,thereby, not requiring a standoff tube 160. The brazing can be done byany means known to one skilled in the art, including but not limited tofurnace brazing at one time or through a manual brazing process.

The heater flange component 120, the perforated wall or skirt of theperforated box assembly 110, and the standoff tubes 160 may be made fromany material suitable for use in an exhaust system; alternatively, theyare made from a metal or metal alloy. A metal joining process, such asbrazing, among others, may be used to join the heater flange component,perforated skirt of the perforated box assembly, and the standoff tubes.One specific example of a metal joining process includes firsttack-welding the components to be joined into position and thenperforming nickel brazing in a furnace. Such a brazing process providesstrength and seals the exhaust, while making all of the joints to thestandoff tubes at one time.

The heating apparatus 110 may be a “smart” heating apparatus and mayinclude a combination of at least one heater element 135 and at leastone thermocouple 10. Optionally, the heating apparatus 101 may furtherinclude a LIN bus, a CAN bus, or other type of bus capable of providinga communication pathway between at least two system components.

A thermocouple 10 may be in contact with the sheath of the heaterelement 135, located on an element support component (e.g., the post143) adjacent to the heater element 135, or located upstream ordownstream of the heater element 135. The thermocouple 10 may be any thethermocouples described previously in this application, such as thoseshown and described in FIGS. 1A and 1B. Additionally, more than onethermocouple 10 can be used.

The thermocouple 10 can measure the temperature in a specific or desiredlocation of the heater element 135. The temperature measurement systemutilized with the thermocouple 10 may be the temperature measurementsystem 20 previously described. The measurement of temperature by thethermocouple 10 allows the heating apparatus 1 to reduce power when theheater element 135 is approaching or surpassing a predeterminedtemperature limit established according to the application beingperformed. The thermocouple 10 may also be used for diagnostic purposes.

A smart heating apparatus provides the benefits of enhanced diagnosticcapability in addition to maximizing heat flux and loweringmanufacturing cost. A robust diagnostic capability often depends on thevariation exhibited from heater element to heater element. A smartheating apparatus that is capable of using performance characteristicsor information for specific heater elements provides for enhanceddiagnostic capability by allowing at least a portion of the randomvariation that arises from manufacturing variances to be corrected orcompensated for. The smart heating apparatus may compensate for athermal gradient present in a diesel oxidation catalyst (DOC), dieselparticle filter (DPF), selective catalytic reducer, lean NOx traps, oranother exhaust component that includes an after-treatment catalyst. Oneskilled in the art will understand that other diagnostic activities mayalso be enabled through the use of smart heating apparatus.

Referring now to FIGS. 9A and 9B, the heating apparatus 101 may furthercomprise a thermowell 155 integrally attached to the post 143 of thebracket assembly 140, such that the thermowell 155 allows indirectand/or direct contact between the heater element 135 and thethermocouple assembly 156. A thermowell 155 is a tubular fitting used toprotect the thermocouple 10 when installed for use in the heatingapparatus 101. The thermowell 55 may also be tubular fitting that isopen on both ends, thereby, allowing the thermocouple 10 to make directcontact with the flowing exhaust gases, while acting as a seal toprevent the escape of the gases when the thermocouple 10 is insertedinto the heating apparatus 101. The thermowell 55 may be placed incontact with any of the posts 143 of the bracket assembly 140.Alternatively, the thermowell 155 may be placed on the second to lastheater element 135 in the heating apparatus 101 because it is typicallyone of the hottest coils and the exhaust gas flows past it immediatelyprior to exiting the heating apparatus 101. When desirable, thethermocouple 10 does not have to actually contact the heater element135. In the illustrated design, the heater element 135 actually contactsthe post 143 and/or U channel bracket 180, while the thermowell 155contacts the post 143 and the thermocouple 10 contacts the thermowell155. One skilled in the art will understand that it is desirable to havea consistent thermal pathway for the life of the product, but notnecessarily for the elements to be in direct contact.

The foregoing description of various forms of the invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formsdisclosed. Numerous modifications or variations are possible in light ofthe above teachings. The forms discussed were chosen and described toprovide the best illustration of the principles of the invention and itspractical application to thereby enable one of ordinary skill in the artto utilize the invention in various forms and with various modificationsas are suited to the particular use contemplated. All such modificationsand variations are within the scope of the invention as determined bythe appended claims when interpreted in accordance with the breadth towhich they are fairly, legally, and equitably entitled.

What is claimed is:
 1. A temperature measurement system comprising: atleast one grounded thermocouple; and a processor in communication withthe at least one grounded thermocouple, the processor being configuredto receive measurements from the at least one grounded thermocouple;wherein the at least one grounded thermocouple is biased by an isolatedvoltage when the processor is receiving a measurement from the at leastone grounded thermocouple.
 2. The system of claim 1 further comprising aplurality of thermocouples, wherein only one of the plurality ofgrounded thermocouples is biased with the isolated voltage when theprocessor is receiving a measurement from the one grounded thermocouple.3. The system of claim 2, further comprising a multiplexer incommunication with the plurality of thermocouples and the processor, themultiplexer being configured to provide measurements taken from one ofthe plurality of thermocouples to the processor.
 4. The system of claim3, wherein the multiplexer is configured to bias at least one groundedthermocouple with the isolated voltage when the processor is receiving ameasurement from the at least one grounded thermocouple.
 5. The systemof claim 1, further comprising an analog-to-digital converter incommunication with the processor and the at least one groundedthermocouple, the analog-to-digital converter being configured toconvert measurements from the at least one grounded thermocouple todigital numbers and provide digital values to the processor.
 6. Thesystem of claim 1, wherein the at least one grounded thermocouplecomprises: a sheath having an open end and a closed distal end having atip, the tip of the closed distal end defining a junction point; and asignal wire extending from the open end to the junction point; whereinthe signal wire and the sheath are made from dissimilar metalsconfigured to produce an electric potential across the signal wire andthe sheath, the electric potential related to temperature at thejunction point.
 7. The system of claim 1, further comprising: a housingcoupled to the least one grounded thermocouple; and a power supplylocated within the housing, the power supply generating the isolatedvoltage.
 8. The system of claim 1, wherein the processor is locatedwithin the housing.
 9. A grounded thermocouple, the groundedthermocouple comprising: a sheath having an open end and a closed distalend having a tip, the tip of the closed distal end defining a junctionpoint; and a signal wire extending from the open end to the junctionpoint, wherein the signal wire and the sheath are made from dissimilarmetals configured to produce an electric potential across the signalwire and the sheath, the electric potential related to temperature atthe junction point.